1. Field of the Invention
This invention relates to the refining of aluminum. More particularly, it relates to an improved two-stage aluminum refining system.
2. Description of the Prior Art
Molten aluminum is commonly refined to remove dissolved hydrogen, non metallic particles and alkaline and alkaline--earth metals by sparging with a gas, such as argon or nitrogen, sometimes with the addition of chlorine. For maximum effectiveness and economy of gas usage, the sparging gas is dispersed in the form of fine bubbles. Such dispersion is advantageously accomplished by the use of a spinning nozzle for the injection of the sparging gas into the molten aluminum. This refining process can be carried out on a continuous or semi continuous basis in a flow-through system. When a fairly high aluminum refining capacity is required, i.e. usually above about 25,000 lbs./hr, it may be desirable to position two or more spinning nozzles in the refining vessel. If two spinning nozzles are used in a single enlarged chamber, the productive capacity of the vessel may be doubled compared to that achieved by the use of a single nozzle vessel. If, however, the nozzles are placed in separate compartments positioned adjacent to each other, in series, within the vessel, the capacity can be increased by a factor of two again compared with the capacity achieved using two nozzles operating within one chamber of the same total size. Such a two stage refining system, in which molten aluminum is passed into the inlet to the first stage at one end of the vessel and is removed from an outlet from the second stage at the, opposite end of the vessel, is further described and illustrated in the Pelton, U.S. Pat. No. 4,373,704. In this system, the separate compartments within the refining vessel are separated by a baffle adapted to enable molten metal flow to occur only from the first chamber to the second chamber, with no reverse flow from the second chamber to the first. It is possible, of course, to construct and use a system incorporating more than two such refining stages.
Aluminum refining systems having two or more stages will thus be seen to have the advantage of reduced size for any given refining capacity, together with enhanced refining effect per nozzle and volume of gas employed. In addition, such multi-stage systems offer opportunities for employing different refining gases in different refining stages. For example when a fairly large amount of chlorine is required for removal of alkaline and alkaline earth metals, all of the chlorine addition can be made in the first stage. Some of the chlorides thus formed in the first stage may be removed in the second stage. This result can not be achieved effectively in a single stage system, even when two injection nozzles are used therein.
The two stage system disclosed in said Pelton patent utilizes an externally heated cast iron tub with an interior lining and baffle means to create the two separate compartments. As illustrated in the drawings thereof, said stages are arranged in series with molten aluminum being passed into the bottom of the first stage at one end of the system, and removed from the top of the second stage at the opposite end of the system.
While the two stage system described above has significant advantages over a single stage system, there is, of course, a general desire in the aluminum refining art for further improvements, such as to provide for easier and more convenient installation, more compact design, particularly in light of the very limited operating space available at many refinery locations, ease of operation and maintenance, and the like.
It is an object of the invention, therefore, to provide an improved two-stage vessel for the holding and refining of aluminum.
It is a further object of the invention to provide a two stage refining system having simplified installation, operation and maintenance features thereof.
With these and other objects in mind, the invention is hereinafter described in detail, the novel features thereof being particularly pointed out in the appended claims.